It is supposed to come by every ten minutes, but sometimes it is longer than that - like when you have been standing on your feet for the last two days, and your legs and back are screaming at you. Not to mention the last 2 hours of being on your feet were spent in the Holocaust Memorial Musuem, which is draining in a whole 'nother way. And chances are, when it does take longer than 10 minutes, there will be no bench around, and even the railing that you want to lean against will have fancy scrolling spikes on top to prevent you from leaning. No kidding.
And then when you do get on that bus, and it is hot, and there is a woman cursing loudly at the driver, and the bus temporarily stops working in a seedy part of town, and you are wondering if you should just get out and walk to the hotel.....